SACO, Maine — A maintenance worker with financial problems killed his wife and three children with a shotgun, then committed suicide over the weekend in what state police called one of the worst cases of domestic violence in Maine history, investigators said Monday. Joel Smith presented a friendly face at the 61-unit apartment complex where he worked. But he was having domestic and financial problems, and his wife told a family friend that he had recently threatened to kill himself, police said. The family had moved from Arizona about two years ago because of the sour economy, said Smith’s mother, Jerys Caruthers-Thorpe, of Scottsdale, Ariz.

“I know something had to have snapped because Joel never would have done that in his right mind,” she said.

Heather Smith, 35, was shot along with the couple’s 4-year-old daughter, Lily, in the parents’ bed, said Sgt. Christopher Harriman, a state police detective. Joel Smith’s body was found on the floor nearby, the shotgun by his side, Harriman said.

The boys, 12-year-old Jason Montez and 7-year-old Noah Montez, were found dead in their separate bedrooms, Harriman said.

No suicide note was found. But investigators said the wife told a family friend Saturday night before the shooting that Joel Smith recently had threatened suicide by holding a gun to his head about a week earlier. The friend later contacted an apartment complex worker to express concerns about the family’s well-being, leading to the discovery Sunday, police said.

The case underscores the importance of taking suicide threats seriously, especially in light of a report by the Maine Domestic Abuse Homicide Review Panel that showed 66 percent of domestic homicide perpetrators had previously exhibited suicidal behavior, said Maine Attorney General Janet Mills.

“Telling your boyfriend or girlfriend, ‘I can’t live without you,’ can quickly cross from the innocuous to the devastating,” she said.

Neighbors described the father as well known in the apartment complex along the Saco River because he worked for a company that provided maintenance services. They described him as friendly and outgoing. Few knew about any problems.

“If there was anything going wrong, no one knew it,” said Heather Nason, who used to babysit the three children. “Whatever was wrong, they hid it well.”

Smith, who was a carpenter and builder, decided to follow his father to Maine in hopes of escaping the tough economy out West, Caruthers-Thorpe said.

Recently, she said, the family had suffered financial problems and her son realized his wife was suffering from an addiction, leading them to consider returning to Arizona.

“They were having problems, serious problems,” she said. “They were in the process of trying to get some help.”

Many people who knew the family described Smith as friendly, an assessment shared by his mother. “He was very talented, and artistic, and a perfectionist, and a very devoted family man,” she said.

The killings of the mother and three children were among the worst in modern history in Maine, said Stephen McCausland, spokesman for the Maine Department of Public Safety.

Mass homicides in Maine have claimed four lives six times since 1941 — most recently in 2006 when a cook killed and dismembered four people in western Maine, McCausland said. There have never been more than four homicide victims at the same time in the state, he said.